Fractures in the Senate could sink the compromise plan to pass the annual defense policy bill.

Senate Minority Leader Mitch McConnell (R-Ky.) on Tuesday dismissed the strategy being pushed by the leaders of the House and Senate Armed Services Committees as a “transparent attempt” to avoid tough votes on imposing stricter sanctions on Iran, a move the Obama administration has said could imperil a deal to curb the country’s nuclear program.

Specifically, McConnell faulted Senate Majority Leader Harry Reid (D-Nev.) for spending this week considering presidential nominations, saying senators ought to be debating amendments to the defense bill under the normal process, “as we always have in the past."

“I question the way the Senate is being run,” McConnell told reporters at the Capitol.

McConnell offered his criticism after Senate Democrats won their first nominations victory after voting in November to do away with the filibuster on most presidential nominations.

The leaders of the House and Senate Armed Services Committees say their expedited compromise strategy is the only way for Congress to finish a National Defense Authorization Act this year, but not everyone agrees. Sen. John McCain (R-Ariz.), who supports the expedited plan, said that members of both parties are dissatisfied with it.

“There are many in my party and in the other side who are objecting to this process,” McCain said, because the sped-up strategy would allow few or no amendment votes.

The top Republican on the Senate Armed Services Committee, Jim Inhofe of Oklahoma, also acknowledged that some of his Republican colleagues weren’t satisfied, but said it was the only path left.

“The only choice is, ‘Do we want a bill or do we not want a bill,’” he told reporters. “It’s clear [that a] lot of the people that would have drawn up the bill differently would have had amendments that they want. [But] when it gets down to, do you want to have a bill or not have a bill, they want a bill.”

That argument might not stop some members who are dissatisfied with the process from trying to block it by working to force the consideration of controversial provisions like an amendment by Sen. David Vitter (R-La.) related to Obamacare or amendments that would curtail the surveillance activities of the National Security Agency.

Sen. Chuck Schumer (D-N.Y.) said that members of the Democratic caucus were briefed on the expedited strategy in a caucus meeting on Tuesday. Asked whether the bill would ultimately pass, he said: “The hope is it will.”

The bill unveiled Monday would authorize funding for the Pentagon above sequestration levels, maintain restrictions on transferring Guantanamo Bay detainees to the United States and take steps to address the epidemic of sexual assault in the military’s ranks.

Top Pentagon officials have said they are counting on the legislation to pass both chambers by year’s end, an outcome threatened by conflicting House and Senate calendars. The House is now scheduled to adjourn for the year on Friday, while the Senate is set to adjourn the following week, on Dec. 20. Military leaders say they’d really like to see it pass before the end of the month.

“Allowing the bill to slip to January adds yet more uncertainty to the force and further complicates the duty of our commanders who face shifting global threats,” Joint Chiefs Chairman Gen. Martin Dempsey said in a letter to Reid and House Speaker John Boehner (R-Ohio). “I also fear that delay may put the entire bill at risk, protracting this uncertainty and impacting our global influence.”

The bill’s fate in the House was also uncertain Tuesday. Republican leaders have not yet committed to bringing the legislation to the floor.

Former House and Senate aides slammed the upheaval surrounding the annual defense policy bill in separate interviews with POLITICO.

“The history here of 51 straight years of having an authorization bill can’t be understated,” said Jeff Green, a former staff director of the House Armed Services Committee. “It’s the last sacred piece of legislation . For many years, members would go home and they could at least say that they supported the troops and came up with a defense policy bill.”

A failure to pass the bill would only cement the dysfunctional reputation of today’s Congress, said John Ullyot, who was the spokesman for the Senate Armed Services Committee under former chairman John Warner.

“It’s another signal that Congress is an unreliable partner and for the first time in more than a half-century is abdicating its basic duty when it comes to our military.”